Potentiometer



W- D. HULBERT POTENTIOMETER July 27, 1965 4 Sheets-Sheet 1 Filed Sept. 12, 1962 INVENTOR. WarrenQHu/berf ATTORNEY 27, 1965 w. D. HULBERT 3,197,726

POTENTIQMETER Filed Sept. 12, 1962 4 Sheets-Sheet 2 INVENTOR. WarrenQHu/berf ATTORNEY July 27, 1965 w. D. HULBERT 7 3,197,726

PQTENTIOMETER Filed Sept. 12, 1962 4 SheetsSheet 3 F1 9. Fig.8. q

I NV EN TOR. WarrenPHU/berf Fig.7. BY 7 TTORNEY United States Patent 3,197,726 POTENTIOMETER Warren 1). Hulbcrt, Hacienda Heights, Calif., assignor to Spectral Electronics Corporation, San Gabriel, Calif., a corporation of Delaware Filed Sept. 12, 1962, Ser. No. 223,229 4 Ciaims. (Cl. 338-464) This invention relates to variable resistors, and more particularly to potentiometers which may be constructed in an exceedingly small size.

The present application is a continuation-in-part of my co-pending application Serial No. 51,879, filed August 25, 1960, now abandoned.

The requirement for variable resistors of the potentiometer type to permit fine adjustment of electrical resistance in electronic and electrical circuits has long been recognized in the prior art and such potentiometers of various sizes and shapes have been developed for this purpose. For example, the rectilinear potentiometer, the lead screw actuated potentiometer and the worm screw and gear actuated potentiometer are known to the prior art. While these prior art potentiometers have been quite successful for the purposes for which they were developed, the various sizes and shapes necessitated by the particular inner mechanisms of each of the different types of potentiometer have caused them to be physically non-compatible with other circuit components such as, for example, transistors, resistors, diodes and the like. Furthermore, as a result of these physical limitations, the prior art potentiometer-s have not been readily adaptable for use in microcircuits applications such as printed circuits.

For the most part, the prior art potentiometers of the types above referred to have required relatively complex interior mechanisms to provide the operation which is required in the electrical and electronic circuits which utilize such potentiometers. As a result thereof, the size of these potentiometers has been greater than desired in some applications and they have not included designs permitting them to be incorporated along with other circuit components and subsequently encapsulated in plastic or other potting compounds to form a complete sealed module for use in computers and the like.

Accordingly, it is an object of the present invention to provide a potentiometer having an exceedingly small size, that is, subminiature, and which is very light in weight and which is mechanically simple, rugged, and inexpensive to manufacture.

It is another object of the present invention to provide a potentiometer which is compatible both as to size and configuration with small size electrical components.

It is another object of the present invention to provide a potentiometer which is readily adaptable for use in printed circuits.

It is another object of the present invention to provide a potentiometer which is housed in such a manner that it may be encased in plastic or other potting compounds along with additional electrical components comprising an electrical or electronic module.

Additional objects and advantages of the present invention will become apparent from a consideration of the following description taken in conjunction with the accompanying drawings in which similar parts are designated by the same reference numerals and which are presented by way of example only and are not intended as a limitation upon the scope of the present invention and in which:

FIG. 1 is a perspective view of a potentiometer in accordance with the present invention;

FIG. 2 is a cross-sectional view of the potentiometer of FIG. 1 taken about the lines 22;

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FIG. 3 is a cross-sectional view of the potentiometer of FIG. 2 taken about the lines 3-3;

FIG. 4 is a cross-sectional view of an alternative embodiment of a potentiometer in accordance with the present invention;

FIG. 5 is a partial view of the structure of FIG. 4 taken about the lines 5-5 thereof;

FIG. 6 is an axial cross-sectional view of another alternative embodiment of a potentiometer in accordance with the present invention;

FIG. 7 is a partial view of the structure of FIG. 6 taken about the lines '77 thereof;

FIG. 8 is a partial, axial cross-sectional view of an alternative embodiment of a portion of a potentiometer in accordance with the present invention;

FIG. 9 is a partial, axial cross-sectional view of a portion of a potentiometer in accordance with the present invention;

FIG. 10 is an axial cross-sectional view of another example of a potentiometer constructed in accordance with the principles of the present invention;

FIG. 11 is a partially exploded perspective view of a portion of the structure illustrated in FIG. 10; and

FIG. 12 is a perspective view of a different portion of the structure illustrated in FIG. 10.

In accordance with one aspect of the present invention, there is provided a potentiometer having a housing which includes a casing and a base and which defines an internal cavity. A resistance element is positioned within the cavity and fixed electrical connection is made to the resistance element. An electrically conductive element is positioned internally of the housing and is electrically attached to means extending through the base to provide an external electrical connection. A bearing surface is also provided internally of the housing. A rotor having a wiper arm afiixed thereto which makes slidable contact with the resistance element is positioned substantially at the center of the housing and includes bearing means which engages the bearing surface. The wiper arm and the electrically conductive element are electrically interconnected to provide an external electrical connection to the resistance element.

In accordance with a more specific aspect of the present invention, the bearing surface and the electrically conductive element above referred to comprise an electrical lead which is semi-rigid and which extends through the base of the housing and into the interior thereof. The rotor includes a member of electrically non-conductive material having an axial opening. The axial opening receives the portion of the electrical lead internal of the housing in such a manner that the rotor is rotatably supported upon the lead substantially at the center of the cavity. The rotor also includes a slotted opening transverse to the longitudinal axis thereof and communicating with the axial opening above referred to. One end of the wiper arm is inserted through the slotted opening and receives the electrical lead in such a manner that the wiper arm is locked in place mechanically between the electrical lead and the axial opening in the rotor and good electrical contact is provided thereby.

Referring now to the drawings, and more particularly to FIG. 1, there is illustrated a potentiometer in accordance with the present invention. As is therein shown, the potentiometer 10 includes a housing having a casing 11 and a base 12. Protruding through and extending from the base 12 are electrical connections 13, 14, and 15 which preferably are electrically conductive leads which are rigid or semi-rigid in nature and which may be plugged into a proper socket member such as, for example, a transistor grid. These leads may be cemented, for example with an epoxy resin, at the base 12 to provide a 3 dust and moisture proof seal for the housing. A slotted head 16 protrudes from the top of the casing 11 and may be utilized to vary the resistance of the potentiometer as .will be explained more fully hereinafter.

Referring now moreparticularly to FIGS. 2 and 3, the internal construction of a presently preferred embodiment of the potentiometer is illustrated. As is illustrated, the housing defines a substantially circular internal cavity :17. The base 12 is preferably a molded plastic material such as a phenolic resin and has an annular ring 18 extending upwardly therefrom. The outer surface-of the annular ring 18 mates with the inner surface of the casing 11 and the juncture therebetween is cemented to provide a dust and moisture proof seal for the potentiometer. The annular ring 18 is reduced in thickness at its upper portion to form an internal ledge 19 upon which a resistance element 20 is supported.

The resistance element 20 is illustrated as a circular mandrel having resistance wire wound thereabout in a conventional manner. It should, however, be expressly understood that the resistance element 20 maybe of any type known to the art such as, for example, a wire wound card, a film or layer of resistive material deposited upon a base therefor in accordance with well-known techniques 'or the like.

Electrical connection is provided to one end of the resistance element 20 by way of a connective lead 21 which is soldered, welded or otherwise electrically connected to the lead extending through the base 12. A similar electrical connection is provided to the opposite end of the resistance element by connective lead 21a which is affixed to electrical lead 14.

Leads 14 and 15 extend through the base 12 and are bent so as to fit within recesses'14a and 15a respectively. Such construction provides a greater surface to which the connective leads 2]. and 21a may be attached to thereby facilitate assembly of the potentiometer. Such construction also provides a more rigidanchor for the leads. v It should also be noted that lead 13 is bent intermediate its end points to provide a substantially horizontal portion which also fits Within a recess 13a in the base 12. As before, such construction provides greater rigidity for the lead 13 and the purpose therefor will become more apparent in the following description. The two ends of the lead 13 extend through the base 12 so that one end thereof extends externally of the housing and the other end extends internally of the housing and into the cavity 17.

That portion of the lead 13 which extends internally of the cavity 17 is positioned substantially at the center of the base 12. The lead 13, as well as the leads 14 and 15, are molded in place in the base member 12. Preferably, however, these leads are pressed into place through openings which are provided therefor at the time the base 12 is molded. Ineithercase, in the presently preferred embodiment of the present invention the lead 13 is preferably held stationary and provides a bearing surface for the rotor 22 which is mounted thereon. Rotor 22 is preferably an electrically non-conductive material such as Teflon, Kel F, a ceramic or the like. The rotor 22 is provided with a substantially axial opening longitudinally thereof and which extends through only a portion of its length. This opening receives the internally extending portion of lead 13 thus providing a post upon which the rotor rotates. A slotted opening 23 is provided through the rotor 22 transverse to the longitudinal axis and communicates with the axial opening which receives the internal extending portion of the lead 13. The'slotted opening 23 receives oneend 24 of the Wiper arm 25 which has the opposite end 26 in slidable electrical contact with the surface of the resistance element 20. A depression 27 is provided in the end 24 of the wiper arm 25 in order to provide mechanical strength and to better support the wiper arm 25 within the slotted opening 23 of the rotor 22. The wiper arm 25 is preferably constructed of precious metal, such as a platinum alloy, or the electrical equivalent thereof, and is stamped from a plate or sheet of the material as one continuous member having the depression 27 and contact 26.

A rotor head 28 includes a flange 31 having a recess 32 therein. Within the recess 32 there is disposed a washer or o-ring 33, which is preferably constructed of silicone rubber, and which provides a dust and moisture proof seal between casing 11 and the internal cavity 17 of the housing. A recess 34-,is provided within the rotor head 28 for receiving the upper portion of the rotor 22 in a press fit or by insert molding or the like. Although the rotor head 28 is illustrated as a metallic substance such as stainless steel, it is to be expressly undertood that it may be an electrically non-conducting material such as nylon or the like and-the rotor 22 and rotor head 28 may be constructedas one integral unit.

In assembling the potentiometer as illustrated in FIGS. 2 and 3, the resistance element 20 is placed upon the ledge 19 of the base 12 having leads therein and the connective leads 21 and 21a are attached to the leads 15 and 14 respectively. The wiper arm 25 is inserted into the slotted opening 23; and the rotor 22 with the wiper arm thus contained is pressed over the internally extending portion of the lead 13. As the rotor is pressed over the lead 13, the lead contacts the end 24 of the wiper arm 25 and forces it into the position as illustrated in FIG. 3. That is, the end 24 of the wiper arm 25 is caused to become depressed and to conform to the surface of the recess provided by the longitudinal axial opening through the rotor 22. In this manner, firm, mechanical locking for the wiper arm 25 is provided between the surfaces of the lead .13 and the longitudinal axial openingthrough the rotor 22. At the same time, positive electrical connection is also provided between the wiper arm 25 and the lead 13. Alternatively, the end 24 of the .wiper arm 25 may have a slight depres sion formed therein during its manufacture. This depression then fits into the recess provided by the axial opening in the rotor 22. In any event the wiper arm is arranged so that positive mechanical locking is effected between the lead 13 and the rotor 22 and good electrical connection is provided. After the rotor 22 is pressed into place, it may be positioned so that the wiper arm slidably contacts the resistance element 20 at the desired position. The O-ring is then dropped in place and the casing 11 is pressed over the annular ring 18 and cemented to provide a dust and moisture proof sealed housing.

It should be noted that the O-ring 33 and the mating surfaces between the casing 11 and the annular ring 18 provide a housing which is sealed against the entry of moisture, dust, or other foreign matter. This sealed housing permits a potentiometer in accordance with the present invention to be completely immersed in a potting compound without fear of leakage. All known prior art devices are subject to such leakage and as a result thereof attempts at potting have been unsuccessful.

If desired, the interior cavity of the potentiometer may be at "least partially filled with a viscous liquid such as silicone grease. The presence of such a liquid aids in damping any vibrations which may occur in the wiper arm contact .with the resistance element if the potentiometer is subjected to severe stress. The liquid also suspends any'wear products that may be generated by use of the potentiometer and thereby prevents them from possibly interferring with the operation v.of the potenti ometer. In addition to the foregoing, the silicone grease provides an excellent lubricant and heat sink which improves the operation and characteristics of the potentiometer.

If such is desired, a potentiometer in accordance with the present invention may include a stop mechanism which, for example, may be an extension 35 of the molded base 12 which extends upwardly from the annular ring 18 so that a projection 36 from the rotor head 28 will contact it at the desired point thereby preventing the wiper arm from rotating past a desired point on the resistance element. The stop mechanism may also include other means well known to the art, such as an inward indentation in the casing 11 and an eccentric rotor head or the like.

The illustrations of the presently preferred embodiment of a potentiometer in accordance with the present invention are greatly exaggerated in size for clarity of illustration and ease of description. A typical potentiometer in accordance with the present invention is no larger in size than the standard transistor and, for example, may have, exclusive of the internally extending portions of the electrical leads, a diameter of .345 inch and a height of .276 inch and a weight of approximately 1 gram. Because of these magnitudes of geometric dimensions, such embodiments of the invention are typically designated as subminiature. Utilizing a housing of the above dimension and a structure such as that above described and shown in the drawings, the potentiometer may have a total resistance of 50,000 ohms and may dissipate 1 watt at 70 C. ambient.

Although in presently preferred embodiments of the invention above described the base member for the housing is constructed of an electrically non-conductive material, it should be expressly understood that in those instances where it is desired to dissipate larger amounts of power the base may be constructed of a material having better heat conduction such as aluminum. When such material is utilized for the base, a very thin insulative material is disposed between the resistance element and the base. An example of such material may be anodized aluminum or the like. Each of the electrical leads extending through the base member are then surrounded by an insulating material which is bonded to the metallic base in accordance with well known techniques as to provide a seal between the lead and the base and yet maintain the base insulated from the electricalconnections. By using a base of the type above described, the potentiometer may dissipate 2 watts at 70 C. ambient.

Referring now more particularly to FIGS. 4 and 5 there is illustrated an alternative embodiment of a potentiometer in accordance with the present invention. As is therein shown there is provided a housing having a casing 41 and a base 42. A resistance element 43 is seated upon a ledge 44 which is molded into the base 4-2 similar to that above described. It should be noted that the resistance element 43 is constructed of an elliptical mandrel or card upon which there is wound a resistance wire in accordance with well known techniques. Appropriate electrical connection is made to the resistance element 43 by way of a connective lead 45 and is carried externally of the housing by lead 46. Similar external electrical connection is provided to the opposite end of resistance I element 43. An electrically non-conductive rotor 22. having a rotor head 47 which is sealed by way of an O- ring 33 is positioned substantially at the center of t e housing upon a spindle 48. The spindle 4-S fits within an axial opening in the rotor 22 and mechanically locks the wiper arm 49 into appropriate pos1t1on to contact the resistance element 413.

It should be noted that rotor 22' does not extend to the top surface of the base 42 but instead is spaced therefrom. The spindle 4S protrudes a short distance from the rotor 22' and seats into a bearing surface 51 at the center of the base. In this manner the spindle 48 positions and supports the rotor 22 so that it is rotatably positioned substantially at the center of the potentiometer. As the rotor is manually rotated the wiper arm slides upon the surface of the resistance element 43. It should be noted that the rotor head 47 is constructed of an electrically non-conductive material.

External electrical connection is provided to the wiper arm in the presently preferred alternative embodiment, by

providing a second arm 52 extending downwardly to slidably engage an electrically conductive collector bar 53 positioned concentrically with the rotor 22' upon the base 42. The collector bar 53 electrically contacts lead 54 to provide the external electrical connection. The .remaining portions of the potentiometer tre similar in construction and operation to that above described.

Referring now more particularly to FIGS. 6 and 7, there is illustrated another alternative embodiment of a potentiometer in accordance with the present invention. As is indicated by the use of the same reference numerals the potentiometer includes, for the most part, structure similar to that of FIGS. 4 and 5. However, particular attention is directed to the manner in which external electrical connections are made to the wiper arm. This external electrical connection is provided by a lead 55 having a cup-shaped bearing surface "56 which receives an extension 57 of the rotor 58. As is illustrated in FIG. 6, rotor 53 is preferably a metallic electrically conductive member. The rotor head 47 is therefore 'an electrically non-conductive material such as Teflon or the like to insulate the Wiper arm from the casing 41. The construction of the rotor head is similar to that above described with respect to FIGS. 2 and 3, and includes provision for an O-ring 33 in order to provide a dust and moisture proof seal. A wiper arm 59 is affixed to the rotor 58 in order to provide slidable electrical contact with the resistance element 4-3. As is illustrated more clearly in FIG. 7, the wiper arm 59 is alhxed to the rotor 58 by spotwelding, soldering or the like. It is therefore seen that in accordance with this embodiment of a potentiometer in accordance with the present invention, electrical contact to the resistance element is provided by way of the wiper arm 59, the electrical conductor which comprises the rotor 58 and through the bearing surface 56 and the extension 57 of the rotor 53 to the external lead 55.

The rotor mechanism in accordance with the present invention may also be constructed in additional alternative forms. For example, as is illustrated in FIG. 8, the rotor may include a non-conductive member 61 having an axial opening :adapted to receive a pin member 62 therethrough. The wiper arm 63 is inserted within a transverse slotted opening which communicates with the axial opening in the rotor 61 and is mechanically locked in place in a manner similar to that above described in connection with FIGS. 2 and 3. The base 64 of the housing has molded as a part thereof an external electrical connection 65 having an inner surface 66. The inner surface 66 provides a bearing surface 67 into which the pin member 62 is seated in bearing engagement to provide support for the rotor 61. The rotor 61 supports the wiper arm 63 which provides electrical connectioin to the resistance element (not shown) which is mounted with-in the housing.

FIG. 9 illustrates another alternative embodiment of the rotor mechanism, and as therein illustrated, includes a rotor 71 constructed of a non-metallic insulating type material having a cap or sleeve 72 about the outer surface thereof. A wiper arm 73 is welded, soldered or otherwise mechanically and electrically connected to the sleeve 72. The sleeve 72 also includes a projection extending therefrom. The base 74 has molded therein an external electrical connection 65 having an inner surface 76 which provides a bearing surface similar to that described in conjunction with FIG. 6. Electrical connection of the rotor construction to the resistance element is provided by way of wiper arm 73, cap 72 and the. extension thereof 70 to the external electrical lead 75. The bearing surface 76 provides mechanical support for the rotor mechanism 71 as well as electriccal connection.

Referring to FIG. 10 an alternative arrangement of the invention is illustrated, in which a non-conductive base support member 80 is formed with a center post 82 which projects upwardly from the base support member 80 into a cylindrical space defined thereby and extending along the cylindrical axis thereof. Disposed about the base of the center post there is shown a slip-ring member 84 which has a substantiallyannular portion 8-6 and a conductor gripping trough portion 88 which extends radially outwardly fromthe annular-portion 86. The upper lips 90 of the trough portion 88 may be crimped over the end of an external conductor'92 which enters the interior of the potentiometer housing through the bottom of the base support member '80. The bottom of the base support member 80 may be relieved in its top surface to form an open depression 94 for holding the crimped trough portion 88 and the end of the conductor 92 securely against any angular displacement about the center post 82. The annular portion 86 above the slip-ring member may be axially distorted as shown in order to provide an axial resiliency in the member for purpose to be discussed below.

Other conductive leads '96, one only of which is illustratedin the sectional figure are similarly brought through the bottom of the base support member 81 and may be terminated in a smaller depression 98 formed in the top of the base support member 80. In all cases the conductive leads are substantially hermetically sealed to the base support member and are mechanically tightly gripped thereby.

The inner diameter of the upper portion 1% of the base support member 80 is enlarged with respect to that at its lower portion 102 at a step which forms an annular ledge 104 between the two cylindrical portions. A toroidal resistance element 106 having an outer diameter approximately equal to that of the inner diameter of the upper portion 100 may be mounted within the portion 100 upon the annular ledge 104. The resistance element 106 may be a wire wound coil or an annularly shaped resistance card. Tap or end connections may be made between electrical points on the toroidal resistance element 106 and the external leads 96.

The outer diameter of the base support member 80 is substantially constant along its cylindrical length ex- 'cept for a lip portion 108 about the periphery of its bottom surface to form a retaining shoulder 11%) for an overall metallic sealing cap 112. The diameter of the inner surface 114 of the sealing cap 112 substantially matches the outer diameter of the portions 100, 192 of the base support member 30. The upper end of the sealing cap is cup-shaped and is substantially closed except for a central opening 116.

Disposed axially between the upper end of the sealing cap 112 and the portion N9 of the base support member 80 is a stop ring member 118 which has the form generally of a short .hollow cylinder with an outer diameter equal approximately to that of the surface 114' of the sealing cap 112. The inner diameter of the ring stop member 118' is approximately equal to that of the upper portion 100. Disposed on the inner surfaceof the ring stop member 118 is a stopping block 120 which extends radially inwardly for a small fraction of the diameter of the ring stop member 118. The particular shape and function .of the stopping block 120 will be discussed in further detail in connection with the subsequent figures. The ring stop .member 118 may be formed integrally with the base support member 80 or may as in the example of the present figure be formed separately and include a series of angularly interlocking keys 122 which secure the ring stop member 118 from angular displacement with respect to the base support member 80 and which will be discussed in further detail below.

Disposed over the center post 828 there 'is shown a rotor 124- which includes a lower substantially cylindrical portion 126 which is axially relieved to form a bore 128 which forms the rotational bearing for the rotor on the center post 82. The upper portion of the rotor 124 may be of enlargedcross-sectional dimension and include a radially extending stopping arm 13% which extends outwardly toward but just short of the inner diameter of the ring stop member 11.8, but beyond-the inwardly extending stopping block 121 The upper surface of the rotor 124 is relieved to define an angular trough or channel 132 which is disposed concentrically about the axis of the cylindrical toroidal components heretofore described including the central opening 116 in the sealing cap 112. A resilient O-ring 134 may be disposed in the trough 132 and compressed axially between the rotor 124 and the inner surface of the upper portion of the sealing cap 112. A rotor position control 136 may include a screwdriver slot and project upwardly from the rotor 124 through thecentrol opening 116 in the sealing cap. The position control 136 may be integrally formed with the rotor 124 or maybe as illustrated in the present figure, a separate structure having a fluted or knurled cylindrical portion 138 which is pressed into a central opening in the top surface of the rotor 124.

A cup-shaped bushing 140 formed of a conductive material is disposed in a press-fitted relationship over the lower cylindrical portion 126 of the rotor :124. The lower end of the bushing is substantially closed except for a central opening about the center post 82 andis nonrotatably secured over the cylindrical portion of the rotor. Thus it may be seen that the lower portions of the cupshaped bushing 140 bear 'in rotationally sliding engagement with the annular portion 86 of the slip-ring member 84. The rotor is thereby compressed axially between the distored annular slip-ring and the axially compressible O-ring 134, thus assuring electrical contact between the bushing and the slip-ring, and a-herrnetic seal between the O-ring, the sealing cap, and the rotor.

Afiixed as by Welding or soldering to the outer cylindrical surface of the conductive bushing 140 is disposed a conductive wiper arm 142 which is radially resilient and is compressed between a positive contact on the inner toroidal surface of the resistance element 106 and the conductive bushing 149.

Referring to FIG. 11 a portion of the structure depicted in FIG. 10 is illustrated in perspective view for clarity. The rotor 124 is shown mounted in a rotational bearing relationship on the center post '82. The channel or trough 132 for the sealing O-ring 134 (not shown in the figure) is illustrated as a depression formed in the top surface of the rotor 124. Extending upwardly from the central portion of the rotor is shown the rotor position control 136. The radially outwardly extending stopping arm 130 is shown projecting to the right as seen in the figure.

The conductive bushing 140 is shown in axially exploded pictorial relationship with respect to its actual position tightly fitted over the lower, cylindrical portion 126 of the rotor 124. The radially resilient wiper arm 142 is illustrated in its somewhat radially extended position from which it would be radially compressed when urged inwardly by contact with the toroidal resistance element 106. The slip-ring member 84 is illustrated at the lower portion of the figure and is seen clearly to include, in this example, an annular portion 86 which is axially slightly distorted and a conductive lead-gripping portion 88 extending to the left, in the figure, and including a pair of lips which may be crimped over the eelctrical conductor to be attached during the assembly of the potentiometer.

Referring to FIG. 12 the base support member 80 is illustrated with its base flange 108, the retaining shoulder 110 and the upper cylindrical portion 100. The external conductive leads 92, 96 are shown projecting from the bottom of the base support member for connection to external circuitry. The bearing, center post 82 is shown projecting upwardly from the bottom of the base support member into the substantially cylindrical space within the base support member and the ring-stop member 118. The angularly interlocking keys 122 are shown in place within matching circumferential key ways in the upper portion of the base support member 80. The stop- 5) ping block 120 is shown extending inwardly from the periphery of the ring-stop member 113 to form a positive stop for limiting the rotation of the rotor 124 by Virtue of the stopping arm 130 extending therefrom.

From the foregoing description of the various embodiments of the potentiometer in accordance with the present invention, it is seen that in each case there is provided a substantially centrally located rotor mechanism which carries a wiper arm which provides a slidable electrical connection to the resistance element. Electrical connection is then provided between the wiper arm and an electrical lead extending through the housing, preferably the base member, to provide an external electrical connection. It should be noted that in each case the rotor is a mechanically simple and preferably unitary member which permits construction of an exceedingly small or subminiature potentiometer. It is also seen that in each case the rotor head and rotor body are constructed of materials in such a manner that the wiper arm is electrically insulated from the casing of the housing.

There has thus been disclosed a potentiometer which is capable of being constructed in exceedingly small that is, subminiature size and which is simple, rugged, inexpensive to manufacture and is compatible with other modern electronic and electrical components, and is adaptable for utilization in printed circuits.

What is claimed is:

1. A potentiometer comprising: a sealing housing having a substantially cylindrical inner wall portion and including a non-conductive base member having a nonconductive supporting bearing post extension disposed within said housing along the axis of said cylindrical inner wall; a toroidal resistance element disposed within and coaxially with said housing along said cylindrical inner wall; a non-conductive rotor member having a substantially cylindrical end portion which is axially relieved and rotatably supported upon said supporting post extension; a conductive cup bushing member disposed rotationally grippingly over said cylindrical end portion of said rotor member and having an axially relieved end portion disposed between said rotor end portion and said nonconductive base member radially closely about said supporting post extension; a radially resilient conductive wiper member conductively afixed to said cup bushing member and disposed in circumferentially slidable electrical contact with said resistance element; an axially resilient conductive slip-ring element having a substantially annular portion disposed about said supporting post member in effective axial compression between said cup bushing member and said base member in slidable electric contact with the former and in non-rotating contact with the latter; means rotatably afiixed to said rotor for revolving said bushing and wiper arm with respect to said base member; a cap member disposed over at least a portion of said base member and said rotor and being aflixed to the former, whereby the latter is actually urged toward said axially resilient slip-ring element, said cap member being centrally relieved to define an access opening for said means for revolving said bushing and wiper arm; an axially compressible sealing means interposed between said cap member and rotor member; and a rotor stop-ring means interposed between said cap member and said base member for limiting the rotational freedom of said rotor member.

2. The invention according to claim 1 in which said rotor member includes a radially extending stopping arm and in which said rotor stoparing means includes a short, hollow, open-ended cylindrical segment which is rotationally secured to said base member and which has an outer said cap member, and further includes a circumferentially diameter approximately equal to the inner diameter of l@ minor, inwardly extending portion of its inner cylindrical surface.

3. A potentiometer comprising: a sealing housing including a substantially cylindrical non-conductive wall and closed end base member which includes a nonconductive supporting post extending from said closed end into the enclosure of said wall and base member along the cylindrical axis thereof; a ring-stop member including a short cylindrical portion whose outer diameter is approximately equal to that of said wall and base member and which is angularly interlocked thereto; a cup-shaped sealing member which is centrally relieved to from an access aperture disposed over said ring-stop member and said wall and base member and being substantially sealed about its cup-lip periphery to said wall and base member, thereby axially securing said ring-stop member to said wall and base member; a rotor having a cylindrical end portion which is axially relieved to define a bore therewithin, which end is disposed over said supporting post whereby the latter is in rotational bearing relationship with said bore; a conductive bushing member angularly securely disposed over said first end of said rotor; a conductive slip-ring element angularly affixed to said base member about said supporting post in rotationally sliding electrical contact with said bushing member; an O-ring sealing disposed concentrically about said axis between said rotor and said cup-shaped sealing member radially continuously about said axis aperture, said O-ring being in axial compression for sealing said rotor to said cupshaped sealing member and for providing positive electrical contact between said slip-ring element and said conductive bushing member.

4. A sealed subminiature potentiometer comprising: a housing having enclosing walls defining a substantially cylindrical internal cavity, a resistance element positioned about the periphery of said cavity, a pair of fixed electrical connections to said resistance element, and extending through said housing, an electrically conductive slip-ring element extending externally of said housing, and defining a substantially annular bearing surface internally of said housing disposed coaxially therewith at the center thereof, a rotor positioned substantially at the center of said housing and upon said bearing surface, a conductive rotor casing disposed over a portion of said rotor, including that portion positioned upon said bearing surface, a wiper arm afiixed to said rotor casing and having slidable engagement with said resistance element, thereby electrically interconnecting said electrically conductive element to a movable point on said resistance element intermediate said pair of fixed electrical conductions, said electrically conductive element and said electrical connections extending through said housing being secured to said housing and forming therewith substantially sealed portions of said enclosing walls, a rotor position control connected to said rotor, and rotation freedom providing sealing means disposed between said rotor and said housing forming therewith a substantially sealed portion of said enclosing walls.

References Cited by the Examiner UNITED STATES PATENTS 2,437,166 3/48 Lodge 338168 X 2,876,319 3/59 Held 338164 2,884,506 4/59 Graustein 338175 2,908,881 10/59 Pitzer 33 8-164 X 2,914,744 11/59 Schendel 33 8-164 2,943,288 6/60 Budd 338-184 3,059,200 10/62 Bamford 338-174 RICHARD M. WOOD, Primary Examiner. 

4. A SEALED SUBMINIATURE POTENTIOMETER COMPRISING: A HOUSING HAVING ENCLOSNG WALLS DEFINING A SUBSTANTIALLY CYLINDRICAL INTERNAL CAVITY, A RESISTANCE ELEMENT POSITIONED ABOUT THE PERIPHERY OF SAID CAVITY, A PAIR OF FIXED ELECTRICAL CONNECTIONS TO SAID RESISTANCE ELEMENT, AND EXTENDING THROUGH SAID HOUSING, AN ELECTRICALLY CONDUCTIVE SLIP-RING ELEMENT EXTENDING EXTERNALLY OF SAID HOUSING, AND DEFINING A SUBSTANTIALLY ANNULAR BEARING SURFACE INTERNALLY OF SAID HOUSING DISPOSED COAXIALLY THEREWITH AT THE CENTER THEREOF, A ROTOR POSITIONED SUBSTANTIALLY AT THE CENTER OF SAID HOUSING AND UPON SAID BEARING SURFACE, A CONDUCTIVE ROTOR CASING DISPOSED OVER A PORTION OF SAID ROTOR, INCLUDING THAT PORTION POSITIONED UPON SAID BEARING SURFACE, A WIPER ARM AFFIXED TO SAID ROTOR CASING AND HAVING SLIDABLE ENGAGEMENT WITH SAID RESISTANCE ELEMENT, THEREBY ELECTRICALLY INTERCONNECTING SAID ELECTRICALLY CONDUCTIVE ELEMENT TO A MOVABLE POINT ON SAID RESISTANCE ELEMENT INTERMEDIATE SAID PAIR OF FIXED ELECTRICAL CONDUCTIONS, SAID ELECTRICALLY CONDUCTIVE ELEMENT AND SAID ELECTRICAL CONNECTIONS EXTENDAND FORMING THEREWITH SUBSTANTIALLY SEALED PORTIONS OF SAID ENCLOSING WALLS, A ROTOR POSITION CONTROL CONNECTED TO SAID ROTOR, AND ROTATION FREEDOM PROVIDING SEALING MEANS DISPOSED BETWEEN SAID ROTOR AND SAID HOUSING FORMING THEREWITH A SUBSTANTIALLY SEALED PORTION OF SAID ENCLOSING WALLS. 